Leptospira with increased antigenic mass

ABSTRACT

The antigenic mass of  Leptospira  cultures can be significantly increased, independent from any increase in biomass, by supplementing  Leptospira  cultures with a specific fatty acid: linoleic acid. This provides advantages in the production  Leptospira  antigens. Also this enables the production of improved Leptospirosis vaccines, that are safer and more effective.

The current invention generally relates to the fields of bacteriology, and to bacterial vaccines. In particular the invention relates to a method for increasing the antigenic mass of Leptospira, to the Leptospira obtainable by that method, and to vaccines and uses of such Leptospira.

The spirochete bacteria of the genus Leptospira belong to the family of Leptospiraceae, and the phylum Spirochaetes. Leptospira are Gram negative, aerobic, motile bacteria, with an elongated, thin, and spiral-shaped form. Pathogenic Leptospira are found worldwide in many types of animals as well as in humans; mammals, such as rodents, wildlife, farm animals, and dogs are the natural reservoirs. The bacteria cause a disease called Leptospirosis, or: Weil's disease. This develops when Leptospira—after infection and transport via the bloodstream—invade all internal organs, and may display a wide range of mild to severe symptoms, even to mortality, and is of an acute or chronic nature. This variability is the reason the disease is often misdiagnosed. Main symptoms are: fever, nausea, and jaundice, resulting from vasculitis leading to renal-, liver-, or pulmonary failure or cardiovascular disease. The Leptospira typically survive in the renal or genital tract of a host, and this way cause horizontal spread which may also give rise to zoonosis, whereby humans become infected from contact with animal urine or with contaminated surface water. For a review, see: P. Levett, 2001 (Clin. Micr. Rev., vol. 14, p. 296). Leptospira are quite stable in nature, and can survive for months under aqueous conditions and at ambient temperatures.

The classification of Leptospira can be confusing with different systems being used: for many years the classification was based on a serologic differentiation, whereby all pathogenic Leptospira are indicated as serovars of the species Leptospira interrogans (sensu lato). In this system, serovars are distinguished by serological testing of the bacteria's main immunogen: the lipopolysaccharide (LPS) on its outer membrane. Currently more than 200 serovars have been described, which are combined into some 25 serogroups.

However, perpendicular to this classification by serotyping, exists a system of genotyping based on molecular biological features, into so-called: genomospecies. In practice, one Leptospira genomospecies can comprise several serovars, and vice versa. For the present case the serologic classification into serovars will be used.

Some Leptospira serovars infect only a specific host species, but most serovars have a wide host range. For example: L. interrogans (sensu lato) serovar Hardjo is associated with infection of bovines, and in swine serovars Tarassovi, Pomona and Bratislava are most often incriminated. However, serovars such as Canicola, Icterohaemorrhagiae, Bratislava and Grippotyphosa can infect swines, canines, and humans.

Detection of Leptospiral infection of a host is possible in a variety of ways. The gold standard is the serologic detection of specific antibodies in a host's serum by the so-called: microscopic agglutination test (MAT). In this test a serial dilution of a patient's serum is incubated with live Leptospira of a specific serovar. When specific antibodies are present in the serum, these will agglutinate the test bacteria, which can be read e.g. by (dark-field) microscope. The test is highly specific, and the MAT is also decisive for the sero-classification of Leptospira isolates. Alternative tests are Elisa (enzyme linked immunosorbent assay), or PCR (polymerase chain reaction).

Treatment of Leptospirosis can be done therapeutically by administration of antibiotics. However, because the disease is frequently misdiagnosed, prophylaxis by vaccination is preferred. Several types of vaccines against Leptospira for animal- or human use are under investigation, but currently only veterinary vaccines are widely available commercially. The species of animals that are routinely vaccinated are pigs, cattle, and dogs. Vaccination then serves both to prevent disease of the host, as well as to reduce zoonotic spread.

Current Leptospirosis vaccines are based on a suspension of inactivated whole bacterial cells, a so-called bacterin, of a strain from a relevant serovar. These vaccines induce an effective immunity of the humoral type, whereby most immuno-protective antibodies are able to agglutinate and thus neutralise Leptospira. The bacteria's immunodominant antigen is the LPS, and specifically: epitopes on oligosaccharide moieties of the LPS. The immunity induced is mainly serovar specific, with some cross-protection among related serovars, for example from within the same serogroup. An example of a Leptospirosis vaccine is: Leptavoid® H (MSD Animal Health), for bovines, comprising a bacterin from a strain of L. interrogans (sensu lato) serovar Hardjo.

However, as most field situations show prevalence of Leptospira from more than one serogroup, therefore many commercial Leptospirosis vaccines are combination vaccines which provide broad protection. An example is the canine vaccine: Nobivac® Lepto4 (Merck Animal Health), which comprises strains from each of the L. interrogans (sensu lato) serogroups: Canicola, Grippotyphosa, Icterohaemorrhagiae and Pomona. Also, Leptospirosis vaccines are often combined with other bacterial- or viral vaccine compounds.

Today Leptospira are routinely being proliferated in in vitro cultures, for research- or diagnostic purposes, but mainly for the production of vaccines. Methods and procedures for the in vitro proliferation of Leptospira have been known for over 50 years, and so are the ingredients that are critical for its relatively simple culture medium. In the 1960's it was established that Leptospira (for in vitro proliferation) require long-chain fatty acids for their nutrition and cellular composition. Also that these long-chain fatty acids are used as the sole source of energy and carbon, as there is no (detectable) consumption of proteins or carbohydrates from the culture medium. Therefore these fatty acids needed to be provided by the culture medium as Leptospira cannot synthesize long-chain fatty acids de novo, nor extend short-chained fatty acids. These insights helped to develop a semi-defined synthetic Leptospira culture medium (Johnson & Gary 1963; Stalheim & Wilson 1964), in which the previous use of up to 10% v/v of whole (rabbit) serum, was replaced by a combination of an albumin fraction and a defined source of fatty acid. This was further developed into the synthetic medium that is still in use today as the standard culture medium for small- or large scale in vitro proliferation of Leptospira: the EMJH medium, as developed by Ellinghausen and McCullough (1965, Am. J. of Vet. Res., vol. 26, p. 45), and modified by Johnson and Harris (1967, J. of Bacteriol., vol. 94, p. 27).

The EMJH medium contains next to essential vitamins, salts and minerals, also 0.125% v/v polysorbate 80, and 1% w/v bovine serum albumin (BSA) (Faine, S., 1994, p. 312, in: Leptospira and Leptospirosis, ed. S. Faine, Boca Raton, Fla., USA, CRC Press).

Polysorbate 80, which is best known by one of its commercial product names: Tween® 80 (ICI Americas, Inc.), is: polyoxyethylene (20) sorbitan monooleate (CAS nr. 9005-65-6). Polysorbate 80 is a non-ionic surfactant that is used extensively as an emulsifier and solubiliser in pharmaceuticals, cosmetics and foods (E 433). In the EMJH medium however it serves as the bacteria's source of long-chain fatty acids, as it conveniently is water-soluble and has a relatively low toxicity for the bacteria. The main component at about 70% v/v of polysorbate 80 is oleic acid (C18:1), but some other fatty acids are also present, mainly: palmitic acid (C16:0), and palmitoleic acid (C16:1), although this is batch- and manufacturer dependent.

In this respect: the designation of fatty acids such as oleic acid as: “C18:1”, is according to the C:D notation, which is a well-known standard shorthand which describes a fatty acid by its main characteristics: the number of carbon atoms in the acyl chain (for oleic acid: 18), and the number of double (unsaturated) bonds (for oleic acid: 1).

As Leptospira in vitro do not consume protein, the main function of the albumin component of EMJH is considered to be the detoxification of the fatty acids in the culture medium that are provided by the polysorbate 80, by reversibly complexing them, while keeping them biologically available.

Serum albumin, next to providing osmotic pressure, is an important transporter protein in the blood for a variety of compounds, such as proteins, lipids, vitamins, small molecules, etc.

Lipids bound to serum albumin contain di- and tri-glycerides, and esters of cholesterol and phospholipids, but most of it (>90%) is in the form of free fatty acids; with “free” meaning: non-esterified, or not covalently linked. Of these free fatty acids bound to albumin, more than 90% are midsize- and long-chain fatty acids in the range of C14-C20, mainly: myristic acid (C14:0), palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and arachidonic acid (C20:4).

Albumins reversibly bind these fatty acids on several binding sites with different affinity. How much, and which type of fatty acid is bound to an albumin sample from a donor, has a wide physiological variation, and is dependant from chemical features of the fatty acid, such as chain length and level of unsaturation, but also on biological features from the donor of the albumin, such as: species, breed, and gender, as well as its nutritional- and activity status.

For commercial BSA's the amount and the type of fatty acids bound are dependent on the production protocol used by a manufacturer, and vary for each batch.

Classical albumin preparations were obtained by a cold-ethanol fractionation (Cohn et al., 1946, J. of the Amer. Chem. Soc., vol. 68, p. 459) to yield the so-called: Cohn fraction V albumin product.

Since then, a wide variety of serum albumin types and -qualities for use e.g. in biochemistry and tissue culture has become available commercially. An extensive review of the variability of serum albumin was made by Janatova (1974, J. of Medicine, vol. 5, p. 149).

Although under experimental conditions more than 10 molecules of fatty acid could be bound per molecule of albumin (Spector & Hoak, 1969, Anal. Biochem., vol. 32, p. 297), physiologically albumin will carry between about 0.3 and 3 mole fatty acid per mole albumin (Hennig & Watkins, 1989, Am. J. of Clin. Nutr., vol. 49, p. 301).

Commercial serum albumins with low amounts of fatty acids, i.e. below 0.1 mole fatty acid/mole albumin, are also available; such albumin products have deliberately been de-lipidated using one of a variety of available techniques, such as extraction with an organic solvent and/or adsorption to charcoal. However, to obtain very low lipid load levels requires aggressive extraction methods at very low pH value, which may result in denaturation of the albumin.

Large amounts of serum albumins for use in industrial scale biological processes, effectively are only commercially available from bovines, as by-product from the meat industry.

Of the different kinds of BSA suitable for use in in vitro cell-proliferation, some are recommended for use with a specific cell-type. One example is BovoLep® BSA (Bovogen, Australia), which is recommended for promoting the growth of Leptospira in culture; this is a standard BSA that was enriched with a number of vegetable fatty acids.

The complete EMJH culture medium then provides all the fatty acids that are known to be critical for the proliferation of Leptospira in culture: palmitic acid (C16:0), stearic acid (C18:0) and oleic acid (C18:1) (Johnson & Gary, 1963, supra).

This EMJH medium allows proliferation of most of the relevant serovars of L. interrogans (sensu lato). Typical conditions for industrial scale proliferation of Leptospira are at 28-30° C., with control of pO₂ and pH, in a standard fermenter vessel with stirrer. Nevertheless, Leptospira proliferate relatively slowly: generation times between 12 and 24 hours have been reported, depending on the virulence, and level of adaptation to in vitro proliferation conditions. As a result: to reach a high biomass the proliferation process takes relatively long, typically 4-7 days, depending on inoculation density, and takes several pre-cultures to prepare sufficient inoculum. This poses a heavy burden on the fermenter capacity of a producer. Also, this extended culture time poses a great risk for a contamination to develop, e.g. by bacteria, yeast, or fungi that have much shorter doubling times.

Consequently, there is a need for improved methods for the production of Leptospira antigens in in vitro cultures.

The literature in the field describes some efforts to improve the proliferation of Leptospira in in vitro cultures. Some adaptations of the EMJH medium have re-introduced serum, or added a further polysorbate, and/or a hydrolysate. However such enriched EMJH media are not generally used in large scale in vitro proliferation of Leptospira, but are used in diagnostics, typically as semi-solid media, to detect and proliferate even low amounts of the most demanding Leptospira strains from clinical specimens.

Typically Leptospira are proliferated in vitro to prepare an inactivated Leptospirosis vaccine. After the proliferation phase, the downstream process generally starts by the inactivation of the final culture product, to produce the bacterin. This can be done in several ways, commonly by chemical inactivation, such as with formalin, thiomersal, betapropiolactone (BPL), or beta-ethanolamine (BEA). A next step often is to concentrate and purify the inactivated culture, e.g. by centrifugation or filtration. The resulting antigen preparation is then formulated into a vaccine.

It is common practice to formulate inactivated Leptospirosis vaccines based on biomass, whereby one animal dose is made to contain a certain number of cells, typically about 10̂9 cells/dose, of a particular serovar. However this cell count cannot be made on the formulated final product, as the (chemical) inactivation damages the bacterial cells. Therefore, the cell number is determined from the final culture, before its inactivation, by counting all intact cells (alive and dead). With this number, it is calculated how many doses/ml can be allotted to the final product after formulation. As a quality control check for the release of the product to the market, the immunological efficacy (a.k.a. the potency) of the final vaccine is verified. The batch potency test currently required by the regulatory authorities is an in vivo assay employing vaccination and challenge in hamsters (e.g. European Pharmacopeia monograph 0447, for a Canine Leptospirosis vaccine).

An in vitro potency test for Leptospirosis vaccine is known (Ruby et al., 1992, Biologicals, vol. 20, p. 259). This is based on quantifying the antigenic mass of the final vaccine by serological assay, using serovar specific antibodies and -standards. Although the correlation between antigenic mass of Leptospira bacterin and immunological potency is well known, the formulation of Leptospirosis vaccines is still based on biomass/dose.

A consequence of preparing Leptospira bacterin vaccines based on biomass, is that such a vaccine dose comprises an amount of protein and other bacterial components that hardly contribute to immunisation, but on the contrary may lead to adverse local and/or systemic vaccination reactions. This problem is exacerbated in the case of vaccines that combine several Leptospiral antigens. In an attempt to improve the safety of Leptospirosis vaccines, additional purification steps in the downstream process are generally applied. A fear of adverse vaccination reactions is also the main reason that no bacterin-based Leptospirosis vaccine for use in humans is generally available to date.

To overcome possible vaccination reactions, some groups have tried to reduce the burden of non-protective and medium-derived vaccine components of a (combined-) Leptospirosis vaccine, by applying adapted media for the Leptospira culture which are low in protein or even protein-free. However, these media must still provide the essential long-chain fatty acids that are required to support Leptospira proliferation. This required a solution for dealing with the inherent toxicity of these fatty acids, as now these could no longer be detoxified by a bulk of protein such as provided by serum or BSA. One approach was to detoxify the polysorbate itself, e.g. by ion-exchange, or by extraction with polyvinylpyrrolidone, or charcoal (Bey & Johnson, 1978, Inf. & Imm., vol. 19, p. 562). An alternative approach is described in WO 2006/113.601, where the toxicity of the fatty acids is limited by supplementing a protein-free culture medium with polysorbate in repeated small quantities, a so-called fed-batch culture process, based on an increase of the biomass at a controlled, submaximal growth rate. Until today no commercial Leptospirosis vaccines based on protein-free cultured Leptospira are commercially available, and conventional vaccines still rely on downstream purification.

Nevertheless, none of these prior art studies reported any effect of the alterations to the culture medium, or to the conditions for proliferation, on the antigenic mass and/or the immunogenicity of the Leptospira produced. Therefore all these in essence are alternative methods for the production of Leptospira biomass.

It is therefore an object of the present invention to provide improvements to the production of Leptospira antigenic mass and provide improved vaccines resulting therefrom.

Surprisingly it was found that this object can be met, and the disadvantages of the prior art can be overcome, by supplementing a culture of Leptospira with a specific long-chain unsaturated fatty acid: linoleic acid. This leads to a rapid and strong increase of the antigenic mass which exceeds any increase in biomass up to 3 fold.

This discovery opens the way to a number of advantageous utilities, such as to generation of Leptospira with increased antigenic mass, which can be used for the production of improved vaccines against Leptospirosis. Because the increase in antigen amount was found to exceed the increase in biomass, therefore there is a net increase of the antigen amount per set amount of bacterial cells, when comparing a supplemented- to a non-supplemented Leptospira culture.

Leptospira that have such an increased antigenic mass, can now be used to prepare vaccines that have the same antigen content as in prior art vaccines, but with a reduced amount of other bacterial- and culture-derived components. This is favourable for the downstream processing, and for the level of vaccination side-effects. Alternatively: vaccines with an increased antigenic mass can now be applied, at the same level of non-specific components as previously. Next to being favourable for the safety of the vaccinated target, it will be apparent to a skilled person that all these improvements also are highly relevant in economic terms.

Further, linoleic acid-supplemented Leptospira cultures now reach a prior art level of antigenic mass several days earlier than previously. Therefore such cultures can now be produced quicker, more economical, and with lesser chance of contaminations, as culture times can now be considerably reduced. Alternatively: if linoleic acid-supplemented Leptospira cultures are allowed to proliferate to a maximal biomass as previously, much increased amounts of antigen can now be harvested.

The present invention enables the improvement of existing culture media for Leptospira proliferation and antigen production, and the rational design of optimal (semi-)synthetic media.

For supplementing a Leptospira culture with linoleic acid, compounds and/or compositions can be used that are either pure or relatively rich in linoleic acid; an economical example are vegetable oils.

In addition, because in Leptospira the processes for production of biomass, and for generation of LPS antigen seem to be separate to a large extent, an uncoupled process-design is now conceivable wherein in an initial stage a high amount of Leptospira biomass is produced, and in a separate, later stage, the Leptospira are induced to produce LPS antigen by supplementing them with linoleic acid. The separation of these two steps then allows for both processes to be separately optimised for their different relevant parameters, such as length of incubation, incubation temperature, etc. This also provides several logistical- and planning advantages, for example by allowing intermediate storage, harvesting and/or purification.

All this was totally unexpected, as linoleic acid is hardly ever mentioned in the prior art in relation to Leptospira proliferation conditions: Stern et al. (1969, Eur. J. of Biochem., vol. 8, p. 101) described that Leptospira incorporate linoleic acid from the culture medium into its cellular membrane lipids. Johnson et al. (1970, Inf. & Imm., vol. 2, p. 286) reported that linoleic acid was one of a list of fatty acids that were present in BSA that was used for proliferating Leptospira cultures, but did not provide specific amounts. Consequently, no items of prior art describe linoleic acid to be of any special relevance for Leptospira, except for its potential toxicity. In particular linoleic acid was never mentioned or suggested to be of special relevance for the generation of Leptospira antigen, specifically of LPS antigen.

On the contrary, the consensus in the prior art in this field is that the relevant fatty acids for Leptospira are palmitic-, stearic-, and oleic acids, and that these are all provided in abundance in standard culture medium by polysorbate 80. This way Leptospira with an ‘adequate’ amount of LPS antigen have been produced for many years, and no attempts have been described or suggested to improve the amount of LPS antigen per unit of Leptospira biomass. There was also no incentive to do so, as Leptospirosis vaccines are routinely formulated based on biomass, therefore maximising the number of Leptospira cells in a culture has always been the main focus in this field, not their antigenic mass.

It is not known why Leptospira require linoleic acid for the production of their LPS antigen, nor in what way linoleic acid is used by Leptospira to generate (part of) the LPS molecule.

Although the inventors do not want to be bound by any theory or model that might explain these observations, the inventors now speculate that in Leptospira the biological processes directed to bacterial proliferation, and those directed to the generation of LPS may rely on partly separate enzyme systems, requiring different nutrients. This aside from the fact that supplementation with linoleic acid may also induce some increase of biomass.

The inventors further speculate that the standard Leptospira culture media currently in use, such as EMJH, only contain an amount of linoleic acid that is suboptimal for the efficient generation of Leptospira antigen; this is independent of the fact that such media do provide an abundance of the fatty acids that are required for the formation of Leptospira biomass. Consequently, in these prior art Leptospira culture media the linoleic acid is rapidly depleted, after which antigen production comes to a halt long before the maximal cell number is reached. This makes that only a part of the capacity of the Leptospira to produce LPS antigen has so far been used.

Therefore in one aspect the invention provides a method for increasing the antigenic mass of a Leptospira culture, the method comprising the step of supplementing said Leptospira culture with linoleic acid.

The “antigenic mass” for the invention is the amount of LPS antigen of a fixed number of Leptospira cells, which can be determined in a serological assay, such as an Elisa. It is expressed herein as a specific antigenic mass: the amount of immunodominant protective antigenic epitopes on the LPS of a fixed number of Leptospira cells. Presented as the number of serological units of Leptospiral LPS antigen per 1×10̂9 Leptospira cells.

The Leptospira cells are counted according to common procedures, before inactivation, and counting all whole cells, alive or dead; this is what is understood as “biomass” for the invention.

Consequently, for the invention the antigenic mass of a Leptospira culture increases when the amount of antigen per Leptospira cell increases, as a result from applying a method according to the invention.

This is opposed to the effect in prior art methods for producing Leptospira antigens by proliferating Leptospira; these focussed on increasing Leptospira biomass, but did not improve the amount of antigen per cell. Consequently, when the biomass increases and the antigen amount does not, that causes a decrease in the ratio of antigen amount/unit of biomass.

Antigenic mass is a well-known term in the field, and is typically determined using a serological assay, such as an Elisa, using antibodies that are specific for the measured antigen, here: Leptospira LPS. The amount of antigen detected in a sample is then expressed in a number of arbitrary units, whereby these units are defined by reference to the amount of antigen in a standard sample, which is for example set to contain 1000 units. Consequently, the absolute value of the score of an antigen amount is arbitrary, as it is dependent on the specific test applied, and the antibodies and the reference sample that were used. What matters however is the relative difference between the scores of samples tested under the same conditions, and against the same reference sample. This can for example be expressed as the difference in antigen amount measured (250 versus 500 Antigen units/ml), or can conveniently be expressed as a percentage. Such a percentage of difference between two samples will also apply when the same two samples are analysed with a different antibody or against a different (but appropriate) reference sample.

The preferred assay for determining antigen amount for use in the invention is an Elisa, which uses antibodies that are specific for the LPS antigen of a particular Leptospira serogroup or serovar. Such antibodies can agglutinate Leptospira in a MAT. Preferably the antibodies are monoclonal antibodies, and the sample is of sufficiently high titre to allow it to be used in dilution.

Protocols and materials for performing an antigenic mass assay for Leptospira have been well known to a skilled person for a long time, are generally available, and are described and exemplified herein in detail. For example, public biological resource centres such as the ATCC (Manassas, Va., USA), or the CNCM (Institut Pasteur, Paris, France) can provide Leptospira bacteria of most serovars, and provide mouse hybridoma cell-lines expressing serovar specific and agglutinating monoclonal antibodies, or their monoclonals, see: Schoone et al. (1989, J. of Gen. Microbiol., vol. 135, p. 73).

Alternatively such materials can routinely be produced in house using standard techniques: bacteria can be obtained from infected humans or animals (applying proper biosafety measures), and these can be characterised using common techniques; the antigen can be produced by proliferation Leptospira using routine techniques; also serovar specific antibodies can be obtained by immunisation of experimental animals, and methods to produce monoclonal antibodies are well known. The skilled person can easily determine the specificity and titre of these antibodies e.g. by performing the well-known MAT.

Also, several governmental institutions and international organisations provide reference samples of Leptospira bacteria, -antigens, and specific antibodies e.g. for assay development. For example the Royal Tropical Institute (Amsterdam, the Netherlands), which is a reference centre for Leptospira for the WHO, FAO and OIE. Also, the USDA (Ames, Iowa, USA) provides standard reference bacterins of the major Leptospira serovars, and supports interested parties with protocols and materials for setting up and performing antigen amount (potency) ELISA's.

Otherwise, the development and/or the routine performance of Leptospira antigen amount assays can be outsourced to one of many (commercial) diagnostic service institutions.

For the invention, “increasing the antigenic mass” has been achieved by a method according to the invention, if a higher antigenic mass is found for a linoleic acid-supplemented Leptospira culture, when compared to the antigenic mass of the same or a similar Leptospira culture that was not supplemented with linoleic acid, under otherwise identical conditions. An increase in antigenic mass with 20% can already be detected with statistical significance using routine techniques, well known to the skilled artisan. Therefore, in a preferred embodiment of a method according to the invention, the increase in the antigenic mass of a Leptospira culture is with at least 20%, as compared to the antigenic mass of a similar Leptospira culture that was not supplemented with linoleic acid. More preferably the increase in antigenic mass is with at least 25, 28, 30, 35, 40, 45, 50, 63, 77, 90, 100, 121, 150, 175, 184, or with at least 200%, in that order of preference. For the invention, “a similar Leptospira culture” refers to a culture of Leptospira that in biologic terms is highly comparable to the culture of Leptospira that it is compared with. For example this could refer to the use of a Leptospira culture from the same isolate, strain or serogroup for making this comparison. The increase in antigen amount per unit biomass observed upon applying a method according to the invention, differed between the serovars tested. This may be serovar specific, or be related to the characteristics of the specific strain-material that was used from that serovar. To achieve the increase in antigenic mass by the method according to the invention, a description and examples are provided hereinafter.

For illustration, exemplary increases of the antigenic mass for strains from different Leptospira serogroups that were observed by the inventors, following application of a method according to the invention, were: for Icterohaemorrhagiae an increase with: 121%, for Sejroe (serovar Hardjo): 184%, for Grippotyphosa: 63%, and for Australis (serovar Bratislava): with 45%. Details are provided in the examples. All these increases are highly relevant economically.

It is well within the routine capabilities of the skilled person to optimise the increase in antigenic mass resulting from linoleic acid supplementation, e.g. by adaptation of the conditions of the culture, of the supplementation, or of the Leptospira used.

“Leptospira” refers generally to bacteria from the taxonomic genus of spirochete bacteria with that name. This includes also Leptospira that are sub-classified therefrom in any way, for instance as a subspecies, strain, isolate, genotype, serotype, serovar, serogroup, variant or subtype and the like. Such Leptospira share the characterising features of their taxonomic family-members such as the genomic, physical, electron-microscopic, and biochemical characteristics, as well as biological characteristics such as physiologic, immunologic, or pathogenic behaviour. Next to serological classification, other determinations can be based on nucleotide sequencing or PCR assays, as known in the field.

It will be apparent to a skilled person that while the bacterial genus that is the subject of the present invention is currently named Leptospira, this is a taxonomic classification which could be subject to change as new insights lead to reclassification into a new or different taxonomic group. However, as this does not change the micro-organism involved or its characterising features, only its scientific name or classification, such re-classified organisms remain within the scope of the invention.

Preferred Leptospira for use in a method according to the invention are Leptospira that are pathogenic to one or more animal species or to humans; more preferred is at least one serogroup selected from L. interrogans (sensu lato) Canicola, Icterohaemorrhagiae, Australis, Grippotyphosa, Pomona, Tarassovi, Sejroe and Autumnalis.

Even more preferred is at least one serovar selected from L. interrogans (sensu lato) Canicola, Portland-vere, Icterohaemorrhagiae, Copenhageni, Bratislava, Australis, Grippotyphosa, Dadas, Pomona, Tarassovi, Gatuni, Hardjo, Saxkoebing and Autumnalis.

A “culture” for the invention is: a composition comprising Leptospira bacteria. The bacteria in a Leptospira culture for the invention can be in different densities or conditions: intact or not, alive or dead, (partially) ruptured or inactivated, etc. The bacteria can be in any cell-cycle phase such as proliferating, resting, or dormant. The culture can be a proliferating culture, where the Leptospira are recently inoculated, early-, mid-, or late exponential or log-phase. Or the culture can be a static or stationary culture, where the Leptospira are in lag phase, or in a harvested, or stored culture.

The composition comprising the Leptospira bacteria can be liquid, solid, or semi-solid, frozen, or freeze-dried. The composition can be a culture medium, or a storage medium, and can comprise a stabiliser, or another pharmaceutically acceptable additive or carrier. Inter alia such a culture comprises a cell-suspension.

In a preferred embodiment, the culture for use in a method according to the invention is in liquid form, as this facilitates the uptake by the Leptospira of linoleic acid.

For the invention the term “comprising” (as well as variations such as “comprise”, “comprises”, and “comprised”) as used herein, refer(s) to all elements, and in any possible combination conceivable for the invention, that are covered by or included in the text section, paragraph, claim, etc., in which this term is used, even if such elements or combinations are not explicitly recited; and does not refer to the exclusion of any of such element(s) or combinations. Consequently, any such text section, paragraph, claim, etc., can also relate to one or more embodiment(s) wherein the term “comprising” (or its variations) is replaced by terms such as “consist of”, “consisting of”, or “consist essentially of”. For the invention “supplementing” has the common meaning of: adding to supply a deficiency, or to reinforce or extend something (from: American heritage dictionary, ed. Houghton Miflin Co., Boston, USA).

The way in which the supplementation of linoleic acid in a method according to the invention is applied, is in principle not limited, as long as the effect of said method can be reached: an increase of the antigenic mass. Thus, for a method according to the invention, supplementing linoleic acid can be done by addition to an existing culture of Leptospira, either once, repeatedly, or continuously. Alternatively, supplementing a culture of Leptospira in a method according to the invention, can be done by providing a certain concentration of linoleic acid at the moment of establishing the culture of Leptospira for the invention. For example by providing a certain concentration of linoleic acid in a culture medium in which a Leptospira culture is to be inoculated and proliferated, or in a washing-, storage-, or incubation medium in which a Leptospira culture is to be kept or treated.

Also, the supplementation with linoleic acid can be at different time points in the lifecycle of the Leptospira, such as in the early, mid, or late stage of an actively proliferating culture, or in a stored sample; and at different densities of the bacterial cells. The linoleic acid can be in different forms, and can be supplemented in different ways. Options for variation and optimisation of these conditions are described and exemplified herein, and are well within the routine capabilities of the skilled artisan.

In a preferred embodiment the supplementing for a method according to the invention is done by adding linoleic acid to a proliferating Leptospira culture, and by adding gradually over time.

For the invention “linoleic acid” refers to the chemical compound that is the fatty acid, or to a derivative thereof, but also to linoleic acid in a mixture or complex, or to a compound or composition that is relatively rich in linoleic acid. A compound or composition is “relatively rich” in linoleic acid, if it comprises linoleic acid in an amount of at least about 5% of its total amount of fatty acids. Preferably at least about 10, 15, 20, 25, 30, 40, 50% of its total amount of fatty acids, in that order of preference.

Determination of fatty acid content, as well as the differentiation into the relative amounts of individual fatty acids, can routinely be done by a skilled person, for example by extraction and gas-chromatography. Examples of compounds and compositions that are relatively rich in linoleic acid, for use in a method according to the invention, are described below.

Linoleic acid is a C18:2, n-6 delta 9,12 fatty acid, with scientific name: 9,12-octadecadienoic acid, and CAS nr.: 60-33-3. Preferably both its double bonds are in the cis form.

Linoleic acid for the invention is not to be confused with linolenic acid, which is a C18:3 fatty acid, with CAS nr.: 463-40-1. Also not relevant for the invention is conjugated linoleic acid or CLA, which is an isomeric product of linoleic acid, and is produced (ergo not consumed) by bacteria such as Lactobacilli, in the rumen of ruminants.

The linoleic acid may be of natural or of synthetic origin, and may be in isolated state or in any degree of purity. Also the linoleic acid may be bound, coupled or esterified to other chemical groups. All these forms are allowable as long as the linoleic acid is biologically available to the Leptospira culture, and the effect of a method according to the invention can be obtained. Preferably the linoleic acid is in a form that is not too toxic for the Leptospira culture, and that can be used in the context of aqueous culture conditions.

A skilled person can readily determine if a linoleic acid derivative, compound or composition containing linoleic acid, can be used in a method according to the invention, or is too toxic or inconvenient, by the details and examples provided herein. For example by testing such a derivative, compound or composition in a representative small scale fermentation of Leptospira, and determining the amount of Leptospira LPS antigen of a certain number of cells, and compare that to the antigen amount of cells from a similar Leptospira culture which was not supplemented with the linoleic acid containing compound or composition.

Examples of linoleic acid (containing) derivatives, compounds and compositions for use in the invention are: pure linoleic acid, as available in a variety of purities from all major suppliers of bio-chemicals. Also the linoleic acid can be bound on or complexed to a carrier molecule, such as a protein or protein complex (e.g. serum or albumin, an enzyme (acyl-CoA), or esterified to a glycerol or cholesterol, or as a lipoprotein, a phospholipid (bound to a phosphate), or a glycolipid or lipopolysaccharide (bound to a carbohydrate moiety). Also the linoleic acid can be present as a minor free acid component in a composition of other fatty acids. Alternative the linoleic acid may be present in a compound or composition relatively rich in linoleic acid, such as a vegetable oil.

As a fatty acid is normally poorly soluble in an aqueous medium, the linoleic acid, or a derivative, or a compound or composition relatively rich in linoleic acid, can be made into a preparation that facilitates its supplementation to a Leptospira culture, so as to make or keep it bioavailable. For example the linoleic acid may be physically dispersed, or chemically emulsified, or mixed with a solvent. It can be combined with a carrier such as a cellulose, cyclodextrin, or cholesterol, or by using BSA or serum as described above; alternatively linoleic acid can be transferred via a particulate adsorbent such as e.g. Celite® or Amberlite® (Spector & Hoak, supra). An advantageous way to supplement a culture of Leptospira with linoleic acid in a method according to the invention, is by supplementing the culture with BSA that was created to comprise a high amount of linoleic acid.

Therefore in a preferred embodiment of a method according to the invention, the linoleic acid is supplemented in the form of a complex to BSA.

Linoleic acid can be loaded onto BSA by simple co-incubation, until the BSA is saturated with linoleic acid. Binding of fatty acid to BSA is temperature and pH dependent, as is known in the art, and described e.g. in: Spector & Hoak (supra), and Ashbrook et al. (1975, J. of Biol. Chem., vol. 250, p. 2333). The load level of linoleic acid on the BSA can conveniently be analysed by gas-chromatography as described below. How much linoleic acid can be taken up by the BSA, depends on the type and the quality of the BSA, as well as on the amount of fatty acid that was already bound. If maximal loading of linoleic acid is desired, BSA can first be de-lipidated by extraction, and then reloaded exclusively with linoleic acid. A BSA that was loaded with (additional) linoleic acid can be used in Leptospira cultures, instead of, or in addition to, the BSA or serum that is already used in the culture medium.

The inventors have found that effective supplementation for a method according to the invention was possible using a BSA that was created to contain at least about 10% w/w of its fatty acids as linoleic acid.

Therefore a preferred composition for supplementing linoleic acid for a method according to the invention, is a BSA preparation comprising at least about 10% w/w of its free fatty acid as linoleic acid; preferably comprising at least 12, 15, 18, 20, 21, 23, 25, 30, 35, 40, 50, 60, 70, 75, 80, 90, 95, or 99% w/w of its free fatty acid as linoleic acid, in this order of preference.

The skilled person will appreciate that when a Leptospira culture is supplemented with linoleic acid according to the method of the invention, using a BSA preparation, this may increase the protein load of the culture, and thus of the vaccine produced therefrom. This could have an effect on the level of vaccination side effects. Such a culture may therefore require a purification step to get rid of excess proteins. However, as such purification is often being applied anyway, therefore the supplementation of linoleic acid in a complex with BSA or serum is a highly effective way to increase the antigenic mass of a Leptospira culture. The linoleic acid(-preparation) can be supplemented to a Leptospira culture according to the method of the invention, in different ways, e.g. as a pulse, or more gradually over time. A pulse supplementation e.g. would be to supplement all the linoleic acid within about 1 hour, and this would be most appropriate in case the culture is static. For proliferating Leptospira cultures most appropriate are a gradual supplementation, which would mean to add all linoleic acid in a time period of between about 1 to about 6 hours. A fed-batch supplementation for a proliferating culture, would mean to have a feed of linoleic acid(-preparation) going for most of the culture duration. In a preferred embodiment of a method according to the invention, a proliferating culture of Leptospira is supplemented gradually or in fed-batch mode. The amount of linoleic acid that is to be supplemented to a Leptospira culture to achieve an increase in antigenic mass, as in a method according to invention, is in principle only limited by what is feasible from practical, economical, and biological perspective. For example practical considerations are that a fermenter vessel with a proliferating culture should not be opened multiple times for adding a supplement, as that may compromise a safe operation and its sterility. On the other hand when the culture that is to be supplemented is not actively proliferating, such as an end culture, or a stored culture, there is much less risk of a contamination overproliferating the culture. Economic considerations are for example the material costs of supplementing a large amount of a pure linoleic acid, or a special linoleic acid-combination product. Biological considerations are that free fatty acids can be toxic to live cells, although that is less of an issue for a static culture. Therefore, when large amounts of linoleic acid are to be supplemented to a proliferating culture in a short period of time, care must be taken to mitigate or prevent toxicity of the fatty acid to the Leptospira, for example by providing the linoleic acid in a complex to reduce toxicity, as described above. Alternatively the linoleic acid can be supplemented gradually over time.

Further parameters to consider are the conditions of each specific case: the amount, status, and type of the Leptospira, as well as the incubation medium, temperature, pH, etc. With the details and examples herein, it is within the reach of a skilled person to vary and optimise the amount and the way in which linoleic acid is supplemented to a Leptospira culture in the context of a method according to the invention.

The Leptospira in a culture seem to consume linoleic acid as soon as they can. See for example FIGS. 3 and 10, which illustrate that linoleic acid is very rapidly consumed and converted into antigenic mass.

This means that the total amount of antigenic mass generated in such a culture is a result of the cumulative total amount of linoleic acid that was available to the culture during incubation. For the invention, the indication of the amount of linoleic acid that is supplemented to a culture therefore refers to the total amount of linoleic acid that was made available during the proliferating or incubation of a Leptospira culture, as if all linoleic acid was available at a single time point. It is expressed as a concentration based on the total volume of the culture. This is independent of the form or volume of the mixture that the linoleic acid was comprised in, and includes additions made by all media components.

Consequently, a skilled person will appreciate that it will often not be possible to actually measure this total concentration of linoleic acid provided to the Leptospira culture. On the one hand because it is a cumulative number from linoleic acid contributions made over time and from different components. On the other hand because the Leptospira culture will already have taken up and processed part of it before the moment of sampling.

For example, the inventors demonstrated that a significant increase of the antigenic mass could be obtained when supplementing a culture of Leptospira according to the method of the invention with linoleic acid, such that 25 μg linoleic acid had been made available per ml of culture, as compared to a culture which had available only about 5 μg/ml.

At higher amounts of available linoleic acid, antigenic masses further increased. At the highest availability level tested, 425 μg/ml linoleic acid in a Leptospira culture, some toxicity was noticeable for some serovars. However this effect was seen when using a preparation of pure linoleic acid for the supplementation, and can be overcome by appropriate detoxification of the linoleic acid in a complex, as described above.

Therefore in an embodiment, the invention provides a method for increasing the antigenic mass of a Leptospira culture, the method comprising the step of incubating said Leptospira culture under conditions in which at least 15 μg linoleic acid/ml was made available to said culture. In a preferred embodiment of a method according to the invention, the method comprises the step of incubating a Leptospira culture under conditions in which at least 16 μg linoleic acid/ml was made available to said culture. More preferably at least 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 35, 37, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or at least 100 μg linoleic acid/ml was made available to said culture, in that order of preference.

In a further preferred embodiment of a method according to the invention, the method comprises the step of incubating a Leptospira culture under conditions in which between about 15 and 1000 μg linoleic acid/ml was made available to said culture. More preferably between about 20 and 500 μg/ml, between about 20 and 300 μg/ml, or between about 25 and 250 μg linoleic acid/ml was made available to said culture, in that order of preference.

In an embodiment the invention provides a method for increasing the antigenic mass of a Leptospira culture, the method comprising the step of supplementing said Leptospira culture with linoleic acid under conditions in which at least 15 μg linoleic acid/ml was made available to said culture; wherein the Leptospira is at least one serogroup selected from L. interrogans (sensu lato) Canicola, Icterohaemorrhagiae, Australis, Grippotyphosa, Pomona, Tarassovi, Sejroe and Autumnalis; and wherein the increase of the antigenic mass of said Leptospira culture is with at least 20%, as compared to the antigenic mass of a similar Leptospira culture that was not supplemented with linoleic acid. In a further aspect the invention provides a Leptospira culture obtainable by a method according to the invention, wherein said Leptospira culture has an increased antigenic mass. Such a Leptospira culture according to the invention differs from a Leptospira culture of the prior art, in that the Leptospira culture has an antigenic mass that is significantly increased resulting from supplementation with linoleic acid as in a method according to the invention. The increased antigenic mass is readily detectable and quantifiable as described: an increase in antigenic mass by 20% or more is significant and detectable, as described above.

The increase in antigenic mass is relative to the antigenic mass of a similar Leptospira culture under similar condition, but which has not been supplemented with linoleic acid as in a method according to the invention, as described above.

Therefore a Leptospira culture according to the invention is characterised in that the antigenic mass of said Leptospira culture is increased with at least 20% as compared to the antigenic mass of a similar Leptospira culture that was not supplemented with linoleic acid. More preferably a Leptospira culture according to the invention is characterised in that the antigenic mass of said Leptospira culture is increased with at least 22, 24, 25, 28, 30, 35, 40, 45, 50, 63, 77, 90, 100, 121, 150, 175, 184, or with at least 200%, in that order of preference, and as compared to the antigenic mass of a similar Leptospira culture that was not supplemented with linoleic acid. A Leptospira culture according to the invention is obtainable by a method according to the invention as described, for example by supplementing Leptospira in a proliferating-, or stationary culture, or a culture harvest, with linoleic acid, a derivative, or a compound or composition that is relatively rich in linoleic acid. This has several advantageous utilities, amongst which in vaccines against Leptospirosis. In a further aspect the invention relates to a Leptospira culture according to the invention, or a preparation of said culture, for use in a vaccine against Leptospirosis. Preferably a Leptospira culture for use in a vaccine against Leptospirosis according to the invention is in the form of an inactivated Leptospira culture according to the invention. For the invention, “a preparation” of a Leptospira culture according to the invention, may be a fragment of such a culture, for example an extract, sonicate, or filtrate, or a subunit from a Leptospira culture according to the invention, such as a part of the outer envelope containing LPS, a purified LPS, or a part of said LPS. Therefore, in a further aspect the invention provides a vaccine against Leptospirosis comprising a Leptospira culture according to the invention, or a preparation of said culture. A “vaccine” for the invention is a pharmaceutical composition comprising an immunologically effective amount of (a preparation of) the Leptospira culture according to the invention, and a pharmaceutically acceptable carrier. The vaccine induces an effective immune-response against Leptospirosis.

A “pharmaceutically acceptable carrier” is intended to aid in the effective administration of a pharmaceutically active compound, without causing (severe) adverse effects to the health of the target to which it is administered. A pharmaceutically acceptable carrier can for instance be sterile water or a sterile physiological salt solution. In a more complex form the carrier can e.g. be a buffer, which can comprise further additives, such as stabilisers or preservatives.

The Leptospiral component of a vaccine against Leptospirosis according to the invention, will induce in the target human or animal an immune response that will assist to prevent, ameliorate, or reduce an infection with Leptospira, or of the intensity of clinical signs of Leptospirosis, as caused by infecting Leptospira. This may be the result of a reduced colonization or of a reduced infection rate by the Leptospira, leading to a reduction in the number or the severity of lesions and effects that are caused by the Leptospira, or by the target's response thereto. In addition, this will reduce the (urinary) excretion of Leptospira, and thereby the spread into the environment, which reduces the chance of zoonotic infections. What constitutes an immunologically effective amount of a vaccine against Leptospirosis according to the invention is dependent on the desired effect and on the specific characteristics of the vaccine that is being used, and the target to which it is to be applied. For bacterin-based Leptospirosis vaccines, which function essentially by a humoral immune response, the correlation is well known between a certain antigenic mass, and the immunoprotective strength of the vaccine in a target. Therefore the determination of an effective amount is well within the skills of the routine practitioner, for instance by monitoring the immunological response following vaccination, or after a challenge infection, e.g. by monitoring the targets' clinical signs of disease, serological parameters, or by re-isolation of the pathogen, and comparing these to responses seen in unvaccinated animals. In a preferred embodiment the vaccine according to the invention additionally comprises a stabiliser, e.g. to protect degradation-prone components, and/or to enhance the shelf-life of the vaccine. Generally such stabilisers are large molecules of high molecular weight, such as lipids, carbohydrates, or proteins; for instance milk-powder, gelatine, serum albumin, sorbitol, trehalose, spermidine, Dextrane or polyvinyl pyrrolidone, and buffers, such as alkali metal phosphates.

Preferably the stabiliser is free of compounds of animal origin, or even: chemically defined, as disclosed in WO 2006/094,974.

Also preservatives may be added, such as thimerosal, phenolic compounds, and/or gentamicin.

General techniques and procedures in vaccinology are well known in the art and are described for instance in governmental regulations such as the Pharmacopeia, and in well-known handbooks such as: “Veterinary vaccinology” (P. Pastoret et al. ed., 1997, Elsevier, Amsterdam, ISBN: 0444819681), and: “Remington: the science and practice of pharmacy” (2000, Lippincot, USA, ISBN: 683306472).

Target subjects for a vaccine according to the invention can be humans or a wide variety of animals that are susceptible to infection with Leptospira. Preferred targets are one or more selected from: human, canine, porcine, bovine, equine, caprine, ovine and cervine. In principle the target may be healthy or diseased, and may be positive or -negative for Leptospira, or for antibodies against Leptospira. Also the target can be of any age at which it is susceptible to the vaccination. However it is evidently favourable to vaccinate healthy, uninfected targets, and to vaccinate as early as possible to prevent any field infection.

A vaccine according to the invention can serve as an effective priming vaccination, which can later be followed and amplified by a booster vaccination.

A vaccine according to the invention can equally be used as prophylactic- and as therapeutic treatment, as it interferes both with the establishment and with the progression of a Leptospira infection or its clinical signs of disease.

The scheme of the application of a vaccine according to the invention to the target can be in single or multiple doses, which may be given at the same time or sequentially, in a manner compatible with the dosage and formulation, and in such an amount as will be immunologically effective.

The protocol for the administration of a vaccine according to the invention ideally is integrated into existing vaccination schedules of other vaccines that the target may require.

The vaccine according to the invention is preferably applied as a single yearly dose.

A vaccine according to the invention can contain an amount of Leptospira from a culture according to the invention, or of the preparation thereof, corresponding to between 1×10̂6 and 1×10̂10 bacterial cells per dose; preferably between 1×10̂7 and 5×10̂9 per dose.

Vaccines according to the invention, can be administered in a volume that is consistent with the target, and can for instance be between about 0.1 and 10 ml in volume. Preferably one dose is between about 0.25 and 3 ml.

A vaccine according to the invention can be administered to a target according to methods known in the art. For instance as a parenteral application by any route of injection into or through the skin: e.g. intramuscular, intravenous, intraperitoneal, intradermal, submucosal, or subcutaneous. Alternative routes of application that are feasible are by topical application, by inhalation, or via the alimentary route.

The preferred application route is by intramuscular or by subcutaneous injection.

It goes without saying that the optimal route of application will depend on the specific vaccine formulation that is used, and on the particular characteristics of the target. It is well within reach of a skilled person to further optimise a vaccine according to the invention. Generally this involves the fine-tuning of the efficacy of the vaccine, so that it provides sufficient immune-protection. This can be done by adapting the vaccine dose, or by using the vaccine in another form or formulation, or by adapting the other constituents of the vaccine (e.g. the stabiliser or the adjuvant), or by application via a different route.

The vaccine may additionally comprise other compounds, such as an adjuvant, an additional antigen, a cytokine, etc. Alternatively, a vaccine according to the invention can advantageously be combined with a pharmaceutical component for example an antibiotic, a hormone, or an anti-inflammatory drug.

In a preferred embodiment, a vaccine according to the invention is characterised in that it comprises an adjuvant. An “adjuvant” is a well-known vaccine ingredient, which in general is a substance that stimulates the immune response of the target in a non-specific manner. Many different adjuvants are known in the art. Examples of adjuvants are Freund's Complete and -Incomplete adjuvant, vitamin E, aluminium compostions, non-ionic block polymers and polyamines such as dextransulphate, carbopol and pyran.

Furthermore, peptides such as muramyldipeptides, dimethylglycine, tuftsin, are often used as adjuvant, and mineral oil e.g. Bayol™ or Markol™, Montanide™ or light paraffin oil, vegetable oils or combination products such as ISA™ from Seppic™ or DiluvacForte™ can advantageously be used. An emulsion can be water-in oil (w/o), oil-in water (o/w), water-in-oil-in-water (w/o/w), double oil-emulsion (DOE), etc.

Preferred adjuvants for a vaccine according to the invention are aluminiumhydroxide, or Saponin, such as: Quil A®, or Q-vac®. Saponin and vaccine components may be combined in an ISCOM® (EP 109.942, EP 180.564, EP 242.380).

It goes without saying that other ways of adjuvating, adding vehicle compounds or diluents, emulsifying or stabilizing a vaccine are also within the scope of the invention. A vaccine according to the invention can advantageously be combined with another antigen into a combination vaccine.

Therefore, in a more preferred embodiment a vaccine according to the invention is characterised in that it comprises an additional immunoactive component.

An “additional immunoactive component” may be an antigen, an immune enhancing substance, and/or a vaccine, either of which may comprise an adjuvant. The additional immunoactive component when in the form of an antigen may consist of any antigenic component of human or veterinary importance. Preferably the additional immunoactive component is based upon, or derived from, a further micro-organism that is pathogenic to the target. It may for instance comprise a biological or synthetic molecule such as a protein, a carbohydrate, a lipopolysaccharide, a nucleic acid encoding a proteinaceous antigen. Also a host cell comprising such a nucleic acid, or a live recombinant carrier micro-organism containing such a nucleic acid, may be a way to deliver the nucleic acid or the additional immunoactive component. Alternatively it may comprise a fractionated or killed micro-organism such as a parasite, bacterium or virus.

The additional immunoactive component(s) may also be an immune enhancing substance e.g. a chemokine, or an immunostimulatory nucleic acid, e.g. a CpG motif. Alternatively, the vaccine according to the invention, may itself be added to a vaccine.

An advantageous utility of a combination vaccine for the invention is that it not only induces an immune response against Leptospira, but also against other pathogens of a target, while only a single handling of the target for the vaccination is required, thereby reducing discomfort to the target, as well as time- and labour costs.

Examples of such additional immunoactive components are in principle all viral, bacterial, and parasitic pathogens amenable to vaccination of a target that is also a target for a vaccine against Leptospirosis according to the invention.

For example, for porcines: porcine circovirus, porcine reproductive and respiratory syndrome virus, pseudorabies virus, porcine parvo virus, classical swine fever virus, Mycoplasma hyopneumoniae, Lawsonia intracellularis, E. coli, Streptococcus spec., Salmonella spec., Clostridia spec., Actinobacillus pleuropneumoniae, Pasteurella spec., Haemophilus spec., Erysipelothrix spec., Bordetella spec., etc.

For bovines: Neospora spec., Dictyocaulus spec., Cryptosporidium spec., Ostertagia spec., bovine rotavirus, bovine viral diarrhoea virus, bovine coronavirus, bovine infectious rhinotracheitis virus (bovine herpes virus), bovine paramyxovirus, bovine parainfluenza virus, bovine respiratory syncytial virus, rabies virus, bluetongue virus, Pasteurella haemolytica, E. coli, Salmonella spec., Staphylococcus spec., Mycobacterium spec., Brucella spec., Clostridia spec., Mannheimia spec., Haemophilus spec., Fusobacterium spec., etc.

For ovines or caprines: Toxoplasma gondii, peste des petit ruminant virus, bluetongue virus, Schmallenberg virus, Mycobacterium spec., Brucella spec., Clostridia spec., Coxiella spec., E. coli, Chlamydia spec., Clostridia spec., Pasteurella spec., Mannheimia spec., etc.

For canines or felines: Ehrlichia canis, Leishmania donovani-complex, Neospora caninum, canine parvovirus, canine distemper virus, canine adenovirus types 1 or 2, canine hepatitis virus, canine coronavirus, canine para-influenza virus, rabies virus, feline calicivirus, feline herpesvirus, feline panleucopenia virus, Clostridium spec., Hepatozoon spec., Borrelia burgdorferi, Bordetella bronchiseptica, Chlamydia spec., and species of Babesia or Theileria.

For humans: Plasmodium, Leishmania, Toxoplasma, varicella zoster virus, HIV, human papillomavirus, measles virus, mumps virus, rubella virus, rabies virus, poliovirus, rotavirus, respiratory syncytial virus, hepatitis virus spec., influenza virus, Haemophilus spec., Streptococcus spec., Corynebacterium spec., Bordetella spec., Neisseria spec., and Clostridium spec.

In an alternate embodiment, a combination vaccine for the invention can advantageously combine Leptospira from more than one serogroup of L. interrogans, For example, for a canine target: L. interrogans (sensu lato) serogroups Canicola and Icterohaemorrhagiae; or: L. interrogans (sensu lato) serogroups Canicola, Icterohaemorrhagiae, Australis, and Grippotyphosa. From these, one or more may be (derived from) a Leptospira culture according to the invention; preferably all are (derived from) Leptospira cultures according to the invention. In a further preferred embodiment of a combination vaccine for the invention, the combination vaccine comprises both one or more Leptospira that correspond to more than one serogroups of L. interrogans, as well as an additional immunoactive component. For example for a porcine target the combination vaccine may comprise: L. interrogans (sensu lato) serogroups Canicola, Icterohaemorrhagiae, Australis, Grippotyphosa, Pomona and Tarassovi, as well as Erysipelothrix rhusiopathiae and porcine parvovirus. In this combination, one or more of the Leptospira may be a Leptospira culture according to the invention; preferably all are Leptospira cultures according to the invention. In a further aspect the invention relates to the use of a Leptospira culture according to the invention, or of a preparation of said Leptospira culture, for the manufacture of a vaccine against Leptospirosis. The “manufacture” of a vaccine for the invention is carried out by means well known to the skilled person. Such manufacture will in general comprise the steps of admixing and formulation of a Leptospira culture according to the invention, or of a preparation thereof, with pharmaceutically acceptable excipients, followed by apportionment into appropriate sized containers. The various stages of the manufacturing process will need to be monitored by adequate tests, for instance by immunological tests for the quality and quantity of the antigens; by micro-biological tests for sterility and absence of extraneous agents; and ultimately by in vitro or in vivo experiments to determine vaccine efficacy and -safety. All these are well known to a skilled person.

A vaccine according to the invention can be manufactured into a form that is suitable for administration to human or animal targets, and that matches with the desired route of application, and with the desired effect.

Well known forms of vaccines are e.g.: a liquid, a gel, an ointment, a powder, a tablet, or a capsule, depending on the desired method of application to the target. Preferably a vaccine according to the invention is formulated as an injectable liquid, such as: a suspension, solution, dispersion, or emulsion. Commonly such vaccines are prepared sterile.

In one embodiment a vaccine according to the invention is based on a Leptospira culture according to the invention that was inactivated. Such a bacterin based inactivated vaccine can now be manufactured for the invention using well known techniques. Therefore, in a further aspect the invention provides a method for producing a vaccine against Leptospirosis, said method comprising the steps of:

a. proliferating a Leptospira culture in an in vitro system,

b. supplementing said Leptospira culture with linoleic acid,

c. inactivating and harvesting said supplemented Leptospira culture, and

d. admixing the inactivated Leptospira culture with a pharmaceutically acceptable carrier.

The method is performed according to well-known procedures for the proliferation, inactivation and formulation of Leptospirosis vaccines. The harvesting is also performed as in the prior art, except that there are now more options to choose the time point for the harvest than in the prior art: when a prior art level of antigenic mass is required, the harvest can now be made earlier than previously.

Alternatively, when a maximal antigenic mass is desired, the culture can first be allowed to proliferate to its maximal biomass, as was done previously, only that now significantly more antigen amount is produced when the culture is supplemented with linoleic acid as in a method according to the invention.

The term “proliferating” has the common meaning of enabling and inducing the Leptospira bacteria to go through a number of cycles of cell division. Proliferating for the invention incorporates the meaning of similar terms indicating an increase in cell-numbers and cell-size, such as ‘growing’, ‘culturing’, or ‘amplifying’. The proliferation phase is preceded by inoculation, and this in turn may be preceded by strain selection, pre-conditioning, and/or and pre-proliferation. An “in vitro system” is a well-known way of deliberate proliferation of Leptospira bacteria outside of a human or animal organism, under controlled artificial conditions. This typically employs a chemostat or fermenter, and a (semi-)defined culture medium. Routinely, several critical parameters of the fermentation will be monitored and adjusted when appropriate, and this can even be automated. Techniques, materials and equipment for an in vitro bacterial cell proliferation system at any scale is well known and readily available from many commercial suppliers to the life-science industry. In a preferred embodiment of a method for producing a vaccine according to the invention, an intervening step is introduced, which allows the process to be run non-continuously. The intervening step is introduced between the proliferating and the supplementing steps, and relates to a harvest, storage and/or purification of the Leptospira culture that were proliferated in the first step. Therefore, in a preferred embodiment, a method for producing a vaccine against Leptospirosis according to the invention comprises between the first and the second step, an additional step comprising harvesting, storage and/or purification, of a Leptospira culture. This intervening step allows for the separate performance and optimization of the proliferating- and the supplementing phases of a method according to the invention. The intervening step is performed in a way that maintains the viability or the biochemical integrity of the Leptospira culture, in way that allows its effective use in the further steps of the method. For example, the harvesting can be done e.g. by centrifugation or dia-filtration. As a result of the harvesting, the Leptospira can be in a more concentrated form. The storage can be performed at a temperature between about 2 and about 30° C. in an aqueous environment. The purification can comprise a refreshment or a replacement of the proliferation medium, for example to provide optimal conditions for the subsequent steps. Each of these manipulations can be performed separate, combined, or subsequently, and in any logical order. In a method according to the invention, a Leptospira culture is supplemented with linoleic acid. However, linoleic acid as an ultrapure chemical may be too expensive for large scale use in the production of a low margin product such as applies to some veterinary vaccines. Therefore the linoleic acid for use in these methods can be supplemented in different forms or purities, such as in a derivative or a compound or composition that is relatively rich in linoleic acid, as was defined above. Therefore, in a further aspect the invention relates to the use of a compound or composition that is relatively rich in linoleic acid for a method according to the invention. The skilled person is more than capable to test and select compounds and compositions that are relatively rich in linoleic acid, and optimize their use in a method according to the invention. A very economical source of linoleic acid for use in a method according to the invention is a vegetable oil, because some of these oils are well known to contain very high levels of linoleic acid, are economically priced, and are available in a quality and purity that is acceptable for use in methods according to the invention. Therefore in a preferred embodiment of a use according to the invention, the compound or composition that is relatively rich in linoleic acid is a vegetable oil. A “vegetable oil” is an oil that is derived from a part of a plant, most often from the fruits and seeds, such as: berries, peas, beans, grains and nuts; alternatively from: leaf, stem, flower, flower bud, root, or beet. The vegetable oil can be isolated from its vegetable source material by pressing, extracting, etc.; methods to obtain and purify vegetable oils have been known from ancient times.

Examples of vegetable oils that are relatively rich in linoleic acid are listed in Table 1. The values given are in % w/w of total fatty acid content, and are approximate averages, which may vary and depend on the plant-variety and on the extraction process used. Reference: U.S. Department of Agriculture, National Nutrient Database for Standard Reference, release 24, Sep. 2011.

TABLE 1 Approximate content (in % w/w of total fatty acid) of linoleic acid in vegetable oils Safflower oil (1) (2) 78% Grape seed oil 73% Poppy seed oil 70% Sunflower oil (1) (2) 68% Hemp oil (1) 60% Corn oil 59% Wheatgerm oil 55% Cottonseed oil 54% Soybean oil 51% Walnut oil 51% Sesame oil 45% Rice bran oil 39% Pistachio oil 33% Peanut oil 32% Almond oil 23% Rapeseed oil (3) 21% Linseed oil (4) 15% Olive oil 10% (1) In these trivial names of the oils the seed is not specified, even though the oil is obtained from the seed. (2) This does not regard the variant of this oil that is high in oleic acid. (3) A variant of rapeseed oil is Canola ® oil, which has a reduced content of erucic acid. (4) Linseed is also known as: flax seed. Also, some more exotic non-food vegetable (seed) oils are relatively rich in linoleic acid; e.g. oils from the seeds of: Firethorn: 70% w/w of total fatty acids; Oregon grape: 52%; and Sarsaparilla: 51%, (S. Özgül-Yücel 2005, J.A.O.C.S, vol. 82, p. 893). Therefore, for the invention, a vegetable oil having at least 25% w/w of total fatty acids as linoleic acid is preferred, more preferably a vegetable oil having at least 30, 40, 50, 60, 70, or even at least 75% w/w of total fatty acids as linoleic acid, in that order of preference. A Leptospira culture according to the invention can advantageously also be used in diagnostic methods. Examples are the use in a diagnostic test for detection of Leptospira specific antibody or -antigen in a test-sample. For example, a preparation from a Leptospira culture according to the invention can be coated on a plate or carrier, or can be used as capture antigen. Alternatively, the preparation can be used as standard reference antigen with a high antigenic mass. The invention will now be further described with reference to the following, non-limiting, examples.

EXAMPLES 1. General Materials and Methods 1.1. Proliferation of Leptospira:

1.1.1 Bacterial Strains, Medium and Pre-Proliferation

A working seed of a strain of L. interrogans was inoculated into EMJH medium and incubated at 29° C. for 3 to 5 days. If needed up to 5 consecutive pre-culture passages could be made, whereby the pre-cultures were visually inspected for sufficient proliferation (turbidity) as criterion for transfer to the next passage. NB: Appropriate biosecurity and containment measures must be applied when working with live Leptospira.

1.1.2 Main Fermentation

All experiments were performed in 0.5, 2 or 20 L working volume, computer-controlled fermenters (Sartorius), which were filled with 0.5, 1 or 10 L sterile-filtered EMJH medium, respectively. The standard EMJH medium contained 1% w/v BSA and 0.125% w/v polysorbate 80. The pH of the medium was 7.4±0.1 at start. The fermenter was inoculated with 5% v/v serogroup Icterohaemorrhagiae pre-culture (passage 5), giving an inoculation density of 2-4×10̂7 cells/ml at day 0. End yields of Leptospira biomass were typically about 1-2×10̂9 cells/ml at day 5 or 6 of incubation when the fermentation was stopped.

During all fermentation experiments the temperature was controlled at about 29° C. The medium was aerated with headspace airflow, and the dissolved oxygen (pO₂) concentration was controlled by automatic variation of the agitation-rate, to maintain a set pO₂ concentration. Temperature, pH and pO₂ concentration were monitored online, but pH and foam formation were not controlled.

In comparative experiments up to 4 fermenters were run in parallel, which started off simultaneously with the same medium and Leptospira inoculum. One fermenter then usually contained only standard EMJH medium and served as reference, while in the others different supplementations of linoleic acid were made.

1.1.3 Supplementation with Linoleic Acid

Supplementation was done either with pure linoleic acid (Sigma Aldrich, >99% pure) as a 10% v/v stock in absolute ethanol (JT Baker). Alternatively, linoleic acid was supplemented by using a BSA that was created with a high level of linoleic acid (high LA BSA). This high LA BSA was used either to replace a standard BSA in EMJH medium, or was used in addition to BSA in the EMJH medium, in which case it was added as a 25% w/v stock solution in sterile water. The high LA BSA or the pure linoleic acid/ethanol supplements were fed to a fermentor over the course of 4 hours, at 0.1-0.2 ml/hour, until the fermentor culture had received a desired total amount of linoleic acid. Different total available levels of linoleic acid have been tested, of between about 5 and 425 μg/ml in the total volume. The fermenter cultures of Leptospira were supplemented at different cell-densities i.e. at early-, mid- or end phase culture. Typical mid-phase cell density was at about 5×10̂8 cells/ml, which was reached during day 2 of the main incubation. Upon supplementation with linoleic acid from the pure linoleic acid in ethanol stock, sometimes a small decrease in pH was noted, which was corrected by applying some NaOH.

1.1.4 Sampling and Off-Line Analyses

Daily 5 ml samples were taken aseptically, directly from the fermenter, for analyses of total cell count (by Petroff-Hausser counting chamber); antigenic mass (by antigen amount Elisa); inactivated cells; and for profiling of the fatty acid type and -relative amounts (by gas chromatography) in the culture medium.

Samples were inactivated with 0.1 or 0.2% v/v BPL, at 29° C. for 16-24 hours. The inactivated Leptospira were tested in an antigen Elisa within 24 hours.

1.2. Antigen ELISA:

The antigenic mass of Leptospira LPS antigen was determined in antigen Elisa's, which were based on a set of serogroup-, or serovar specific, agglutinating, mouse monoclonal antibodies (moabs), which had been obtained from the: WHO/FAO/OIE and National Collaborating Centre for Reference and Research on Leptospirosis, Department of Biomedical Research, Royal Tropical Institute, Amsterdam, The Netherlands. The moabs used are listed in Table 2. For a reference see: Hartskeerl R. A., et al., International course on laboratory methods for the diagnosis of Leptospirosis, 4th Edition, 1 Apr. 2004. Royal Tropical Institute, Amsterdam.

The Elisa's were set up as capture assays, whereby the same moab was used for coating and for detection.

TABLE 2 Moabs used for the antigen Elisa of L. interrogans (sensu lato). serogroup serovar moab Canicola Portland-vere F152C11 Icterohaemorrhagiae Copenhageni F12C3 Australis Bratislava F81C3 Grippotyphosa Dadas F71C9 Pomona Pomona F43C9 Tarassovi Gatuni F151C8 Sejroe Hardjo F22C6

1.2.1 Preparation of Monoclonal Antibodies for Coating

The moabs for use in the antigen Elisa could be derived from ascites or from cell culture. Both types were purified prior to use by a standard non-chromatographic method. In short: albumin and other non-IgG proteins were precipitated with caprylic acid. Next, the IgG fraction was precipitated with ammonium sulphate. With this method it was possible to isolate more than 80% of the IgG with a purity equal to IgG purified by anion-exchange chromatography.

Alternatively, the moabs could be purified by protein-G column chromatography.

1.2.2 Preparing Conjugated Monoclonal Antibodies

For the antigen Elisa's Horse Radish Peroxidase (HRP)-IgG conjugates were prepared from the moabs, using standard procedures. Basically, the reaction involved a periodate oxidation of the carbohydrate residues of the HRP enzyme to form aldehyde groups, which subsequently reacted with free aminogroups on the monoclonal IgG molecules.

1.2.3 Preparation of Antigen Amount Reference Standards

A reference standard was prepared for each Leptospira strain that was tested by antigen Elisa. The standard is a batch of monovalent Leptospira antigen, from inactivated cells. This is prepared using common techniques, essentially by proliferation a specific strain of Leptospira in EMJH medium as described above, and is inactivated as described before. Next the standard is concentrated and/or diluted in phosphate buffered saline, to contain about 1×10̂9 cells/ml. An arbitrary number of antigen units is affixed to the sample, for example: 1000 Units/ml. When the standard needs replenishing, a subsequent preparation of the same standard, is compared and titrated alongside the old standard several times, before replacing it.

1.3. Fatty Acid Analysis:

Fatty acid compositions and -amounts were tested from samples of Leptospira cells, culture medium components, and from complete EMJH culture medium samples, according to well-known procedures.

The extraction of fatty acids was done as published by Bligh & Dyer (1959, Can. J. of Biochem. Physiol., vol. 37, p. 911) and Morrison & Smith (1964, J. of Lipid Res., vol. 5, p. 600). In short: a 0.5 ml sample was tested, containing either pure complete culture medium, or a sample diluted in water: of Leptospira cells (between 1×10̂9 and 1×10̂10 per 0.5 ml; the cells had been BPL inactivated), or of 1% w/v of a BSA sample. This 0.5 ml was extracted with 1 ml of methanol and 2 ml of chloroform, by mixing for 3 minutes. Another 0.5 ml of water was added, mixed for 30 sec., and the sample was centrifuged for 10 min. at 1.000×g at 2-8° C. The 2 ml chloroform (lower) phase was transferred to a glass vial, and the chloroform was dried off under an N₂ gas stream. The dried lipids were re-dissolved in 0.6 ml BF3 in methanol, and heated for 15 min. at 95° C., which methylated the fatty acids. Next 0.3 ml water and 0.3 ml hexane were added, this was mixed by shaking, after which the hexane (upper) phase was transferred to a standard gas chromatography set-up for analysis of the profile, and the relative amounts of the fatty acids in the extract. As internal standard a sample of C21:0 fatty acid (Heneicosylic acid) of known concentration was used. Normally the samples were measured in duplo, and samples were prepared and measured in containers of glass.

2. Comparison of Prior Art Proliferation Conditions

As a comparative example, the formation of antigenic mass in a Leptospira batch culture under standard prior art conditions (thus without supplementation) was analysed. Leptospira of serogroup Icterohaemorrhagiae were cultured in standard EMJH medium, that had been completed with polysorbate 80 (Croda), and a standard commercial BSA (Millipore). After several rounds of pre-proliferation a main fermenter culture was inoculated and run for 5 or 6 days. For Leptospira of serogroup Icterohaemorrhagiae, the antigenic mass obtained in these conditions of proliferation, was usually between 500 and 700 Antigen Units (of serogroup Icterohaemorrhagiae) per 1×10̂9 cells, as the average over days 3-5.

When such a batch of Leptospira antigen was tested in an in house in vitro potency assay, it failed to reach the required minimal potency level.

This problem was not solved by using in EMJH medium a commercial BSA that was specially recommended for Leptospira culture: BovoLep® BSA (Bovogen, Australia). This was tested next to BovoStar®, which is a standard all-purpose BSA from the same manufacturer, and next to the BSA (Millipore) that was used before. Results are presented in Table 3. “na” is: not available.

Interestingly, BovoLep® did increase the biomass of Leptospira, as advertised, but it had no significant effect on their antigenic mass. This typifies the classical approach to Leptospira proliferation up till today: a focus on the biomass levels.

TABLE 3 Results from use of different BSA ingredients in EMJH medium: C18:2 total Cell numbers at Ag U/10{circumflex over ( )}9 cells/ml, fermenter conditions conc. μg/ml 3 days at 3 days BSA, Millipore 5 1.6 × 10{circumflex over ( )}9 525 BSA, BovoStar ® na 1.6 × 10{circumflex over ( )}9 533 BSA, BovoLep ® na 1.8 × 10{circumflex over ( )}9 498

3. Effect of Linoleic Acid

Only when more linoleic acid was made available to Leptospira cultures, did the antigenic mass increase.

The standard EMJH medium as tested and described above was found to provide about 5 μg/ml of linoleic acid (see Table 3). This was mainly derived from the 0.125% polysorbate 80, as the 1% standard BSA provided less than 1 μg/ml linoleic acid, close to the detection limit of the gaschromatographic analysis.

In this respect, Polysorbate 80, as defined by the Pharmacopeia, is allowed to contain linoleic acid to a maximum of 18% of its fatty acids. However in practice it was found to carry much less, typically less than 1.5%. From one common type of polysorbate 80 (type: Vegetable Grade, from: Croda, France) the inventors compared the linoleic acid content from 48 batches over several years, and found that the average amount of linoleic acid was about 0.3% w/w of total fatty acids. Assuming that polysorbate 80 consists essentially of fatty acids, then the 0.125% v/v of polysorbate 80 that is used in EMJH medium, provides about 4 μg/ml linoleic acid to the culture.

A BSA was created that comprised an increased amount of linoleic acid. Use of this high LA BSA at 1% w/v in EMJH medium provided about 21 μg/ml linoleic acid to a Leptospira culture; with the contribution of the polysorbate such a culture medium provided 25 μg/ml linoleic acid to a fermentor culture of Leptospira. This increase in the available linoleic acid amount, strongly increased the generation of Leptopsiral antigen, to an antigenic mass of 1636 Ag U/1×10̂9 cells (average of days 3-5). This way the inventors have demonstrated the utility of their discovery: the antigenic mass of a Leptospira culture could be increased with 124%, when a Leptospira culture was supplemented with 25 instead of with 5 μg/ml linoleic acid. FIGS. 1 and 2 depict the results of analyses of daily samples from a proliferating Leptospira culture with linoleic acid supplementation, using high LA BSA in the EMJH medium. In FIG. 1 the biomass (left vertical axis) showed a steady increase over all six days of proliferation. The antigen amount (right vertical axis) reached much higher levels than could be obtained from using standard BSA in the culture medium. Nevertheless, the antigenic mass did not increase much after day three. FIG. 2 displays the reason, in the fatty acid profile of the medium from this culture, which clearly demonstrates the relevance of linoleic acid in this context; results are in % w/w of total fatty acids. Please note that the levels of C16:0 (palmitic acid), C18:0 (stearic acid), and C18:1 (oleic acid) relate to the left vertical axis, while the level of C18:2 (linoleic acid) relates to the right vertical axis.

FIG. 2 displays essentially unchanged amounts of C16:0, C18:0, and C18:1 fatty acids in the culture medium over the course of the culture, whereby C18:1, from polysorbate 80, forms the bulk of the total amount of fatty acid. However, the level of C18:2 shows a strong drop over the first three days, and is below the detection limit (s 0.3%) on days 3-5. The exhaustion of the linoleic acid coincides with the reduction of the increase in antigen generation, as shown in FIG. 1.

4. Further Supplementation of Linoleic Acid to the Leptospira Culture

If further linoleic acid is supplemented, the antigenic mass can be further increased.

In a similar culture as described above, linoleic acid was supplemented at mid-exponential phase, on day 2, with pure linoleic acid, diluted in ethanol. An amount of linoleic acid was added that provided 100 μg/ml linoleic acid in the culture. As the fatty acid profiling of FIG. 3 displays, after the rapid initial decrease, and the clear spike resulting from the supplementation on day 2, linoleic acid levels steadily decreased again upon continuation of the culture. The levels of C16:0 and C18:1 fatty acids were assayed as internal references, but these were largely unchanged as expected.

The antigenic mass produced in this experiment for Leptospira from serogroup Icterohaemorrhagiae was 1767 Ag. U/1×10̂9 cells (average of days 3-5).

5. Comparative Cultures with Different Supplementation Conditions

In more elaborate experiments, of the same set-up as in previous Examples, comparative fermenter cultures of Leptospira from serogroup Icterohaemorrhagiae were run side by side, wherein different conditions of linoleic acid supplementation were compared. To highlight the effect of the linoleic acid supplementation, a standard BSA was used in the EMJH medium. In some fermenters linoleic acid was supplemented in mid-exponential phase, either in pure form in ethanol, or as a complex to BSA, by addition of a solution of a high LA BSA.

The amounts of linoleic acid supplemented were 50, 75 and 150 μg/ml. Table 4 lists also the total amount of linoleic acid made available to the cultures.

For all fermenters, daily samples of cells and medium were taken and analysed. Results are presented in FIGS. 4 and 5, and in Table 4 below. The antigenic mass values are based on averages for days 3-5 of the cultures. Also the relative increase in antigenic mass for the different supplementations is expressed as a percentage relative to the un-supplemented culture with standard BSA. The term “non-supplemented” refers to a culture employing standard BSA in EMJH.

TABLE 4 Effect on Leptospira antigenic mass from different supplementations with linoleic acid Ag. mass, average of days 3-5 relative C18:2 total Ag U/ Ag. mass fermenter conditions conc. μg/ml 10{circumflex over ( )}9 cells/ml (%) non-supplemented, stand. BSA 5 729 100 supplem. pure C18:2, 75 80 1450 199 supplem. pure C18:2, 150 155 1550 213 supplem. high LA BSA, 50 55 1612 221 As is clear from Table 4, and from the corresponding graphs in FIGS. 4 (biomass) and 5 (antigen amount), there is a rapid and significant increase in the antigenic mass of Leptospira when the culture is supplemented with linoleic acid, which is not observed in an un-supplemented culture. Some increase in biomass occurs upon supplementation of linoleic acid, but the increase in antigenic mass exceeds that significantly. The increase in antigenic mass is somewhat higher when the culture is supplemented with 150 μg/ml, as compared to supplementation with 75 μg/ml. However, there was not much difference between when the linoleic acid was supplemented in pure form, or as complex with BSA. Possibly this is a trade-off between increase of antigenic mass versus some toxicity. Further favourable effects can be deduced from FIG. 5: the increased antigenic mass can now be reached much quicker through supplementation with linoleic acid. For example, FIG. 5 shows that with supplementation of linoleic acid, a high antigenic mass can be reached within hours from the supplementation.

Also, when the maximal antigenic mass levels that were finally obtained are compared, it is evident that when supplemented cultures are run for the same length of time as previously, then considerably increased amounts of antigenic mass can be obtained.

6. Confirmation of Supplementation Effect in Leptospira of Different Serogroups

In a next study it was confirmed that the increase in antigenic mass upon supplementation with linoleic acid is a general phenomenon in Leptospira. In several experiments cultures of Leptospira strains from several serogroups were proliferated in fermenters in similar set-ups as before and with a similar supplementation: in EMJH medium with either standard BSA or with high LA BSA; some cultures were further supplemented with 100 μg/ml linoleic acid, from pure linoleic acid in ethanol. Results of analyses of biomass and antigen amount are presented in FIGS. 6-7 (Sejroe), and 8-9 (Grippotyphosa), and are summarised in Table 5.

TABLE 5 Confirmation of effect on antigenic mass by supplementation with linoleic acid for Leptospira from different serogroups Antigenic mass, C18:2 2 day average total Ag U/ relative conc. 10{circumflex over ( )}9 cells/ Ag. mass Serogroup fermenter conditions μg/ml ml (%) Sejroe non-supplemented 5 — — high LA BSA 25 287 100 supl. pure C18:2, 100 125 814 284 Grippotyphosa non-supplemented 5 — — high LA BSA 25 5074 100 supl. pure C18:2, 100 125 8286 163 Australis non-supplemented 5 8862 100 high LA BSA 25 — — supl. pure C18:2, 100 105 12822 145

For Leptospira from serogroup Sejroe (serovar Hardjo), supplementation with 100 μg/ml linoleic acid of high LA BSA culture medium resulted in an increase of the antigenic mass with an impressive 184%. Some increase in biomass was observed after supplementation, but the increase in antigen amount was much higher. The fermenter was run for 6 days, and scores for these experiments were averaged over days 5 and 6 of the culture.

For serogroup Grippotyphosa the scores were averaged over days 4 and 5 of the culture. An increase with 63% was observed in the antigenic mass, resulting from the supplementation with linoleic acid.

Similarly, for serogroup Australis (serovar Bratislava), an increase in antigenic mass with 45% was observed; here the low LA BSA medium was used for supplementation.

7. Maximum Supplementation Levels

In one study the maximal level of linoleic acid supplementation was investigated: Leptospira from serogroup Icterohaemorrhagiae were cultured in EMJH with high LA BSA, and supplemented with 100, 200 or 400 μg/ml linoleic acid, from pure linoleic acid in ethanol. From the results it was apparent that the addition of 400 μg/ml induced toxicity for the bacteria, as cell numbers decreased rapidly after supplementation. Therefore this experiment will be repeated by giving a similarly high level of linoleic acid supplementation, but then from linoleic acid in a complex with BSA that has been saturated with linoleic acid. The stimulatory effect of the 100 μg/ml supplemented group was as observed before, while the 200 μg/ml group gave slightly less increase of the antigenic mass compared to that of the 100 μg/ml group.

Consequently, under these conditions supplementation with pure linoleic acid seems to be optimal when between 25 and 250 μg/ml linoleic acid is made available to a culture of Leptospira.

8. Time Point for Supplementation

In further experiments the relevance of the time point for the supplementation of a Leptospira culture was determined. Using Leptospira of serogroup Icterohaemorrhagiae, suppletion-time points tested were early-, mid- and late exponential phases. EMJH medium with standard BSA was supplemented with 100 μg/ml pure linoleic acid in ethanol. The total amount of linoleic acid made available to these cultures was therefore 105 μg/ml.

Results are presented in Table 6 and FIG. 10. As FIG. 10 demonstrates, an acute increase in antigenic mass can be induced at all phases of the Leptospira culture, with a very rapid climb already at 2, 4, and 8 hours after the suppletion. With this time scale, the increase results mostly from a biochemical process, and less from proliferation.

The fact that the amount of antigen produced seems to be lower when the supplementation is done later, derives from the slight positive effect that the linoleic acid supplementation has on the biomass. This is levelled out when expressing the antigenic mass per standard cell amount, see Table 6.

TABLE 6 Effect of linoleic acid supplementation at different phases of proliferation of a Leptospira culture. Ag. mass, average of days 4-5 relative C18:2 total Ag U/ Ag. mass fermenter conditions conc. μg/ml 10{circumflex over ( )}9 cells/ml (%) non-supplemented, low LA BSA 5 789 100 1 × 10{circumflex over ( )}8 cells/ml, 100 105 1783 226 5 × 10{circumflex over ( )}8 cells/ml, 100 105 1564 198 9 × 10{circumflex over ( )}8 cells/ml, 100 105 1656 210 Tests of supplementation at further time points: after harvest, after wash and after concentration, are on-going. The incubation of end phase cultures may require medium refreshment; nevertheless the supplementation of an end phase culture is estimated to be most favourable, because in that stage the cells are in high numbers, and are still capable of antigenic mass formation. In addition in this stage it is less relevant if any residual toxicity of the supplemented linoleic acid would interfere with the cells' capacity to proliferate as that is no longer required.

9. Determination of Improved Immuno-Potencv of Vaccines Prepared from Supplemented Leptospira Cultures

Leptospira cultures that were supplemented with linoleic acid have been produced, as described above. These will be formulated into inactivated adjuvated Leptospirosis vaccines as is well known in the art, and tested in in vivo experiments as prescribed in the Pharmacopeia monographs. Effects of seroresponse, challenge protection, and level of adverse vaccination reactions will be monitored.

Because for Leptospirosis vaccines the correlation between antigenic mass and immuno-protective capacity is well known, it can be predicted with certainty that bacterin vaccines having a higher antigenic mass than previously, will also induce higher levels of immune-protection.

Similarly, because the protein load of Leptospira bacterin vaccines is clearly implicated as the causative effect of vaccination side-effects, it can also be predicted that Leptospira bacterin vaccines having less protein, but equal antigenic mass as previously, will induce fewer side effects, but an equal, or probably improved, immunisation.

LEGEND TO THE FIGURES

FIG. 1:

Results of biomass and of antigen Elisa over time, on a culture of Leptospira from serogroup Icterohaemorrhagiae in EMJH medium containing high LA BSA that was not further supplemented.

FIG. 2:

Results from analyses of the fatty acid profile in the culture medium of the culture represented in FIG. 1.

FIG. 3:

Fatty acid profile of the culture medium from a culture of Leptospira from serogroup Icterohaemorrhagiae in EMJH with high LA BSA, whereby the culture was supplemented with 100 μg/ml linoleic acid at a cell density of 5×10̂8 cells/ml on day 2

FIGS. 4 and 5:

Respectively the biomass and the antigen amount measurement results from different cultures of Leptospira from serogroup Icterohaemorrhagiae, proliferated in EMJH medium with standard BSA; the cultures were either un-supplemented as reference culture, or supplemented with linoleic acid: one with 75 μg/ml of linoleic acid, from pure linoleic acid in ethanol; one with 150 μg/ml, also from pure linoleic in ethanol, and one with 50 μg/ml linoleic acid, as BSA-complexed linoleic acid.

FIGS. 6 and 7:

Respectively the biomass and the antigen amount measurement results from different cultures of Leptospira from serogroup Sejroe (serovar Hardjo), proliferated in EMJH medium with high LA BSA; the cultures were either un-supplemented as reference culture, or supplemented with 100 μg/ml linoleic acid from pure linoleic acid in ethanol.

FIGS. 8 and 9:

Respectively the biomass and the antigen amount measurement results from different cultures of Leptospira from serogroup Grippotyphosa, proliferated in EMJH medium with high LA BSA; the cultures were either un-supplemented as reference culture, or supplemented with 100 μg/ml linoleic acid from pure linoleic acid in ethanol.

FIG. 10:

Effect on the increase in antigenic mass when a culture of Leptospira is supplemented at different stages of proliferation. Leptospira from serogroup Icterohaemorrhagiae were cultured in standard EMJH medium, and supplemented with 100 μg/ml linoleic acid, at early-, mid-, or late stage. Initial sampling was at 2, 4, and 8 hours after supplementation. 

1. A method for increasing the antigenic mass of a Leptospira culture, the method comprising the step of supplementing said Leptospira culture with linoleic acid.
 2. The method according to claim 1, the method comprising the step of incubating a Leptospira culture under conditions in which at least 15 μg linoleic acid/ml was made available to said culture.
 3. The Leptospira culture obtainable by a method according to claim 1, wherein said Leptospira culture has an increased antigenic mass.
 4. The Leptospira culture according to claim 3, or a preparation of said culture, for use in a vaccine against Leptospirosis.
 5. A vaccine against Leptospirosis comprising a Leptospira culture according to claim 3, or a preparation of said culture.
 6. A method for producing a vaccine against Leptospirosis, said method comprising the steps of: a. proliferating a Leptospira culture in an in vitro system, b. supplementing said Leptospira culture with linoleic acid, c. inactivating and harvesting said supplemented Leptospira culture, and d. admixing the inactivated Leptospira culture with a pharmaceutically acceptable carrier.
 7. The method according to claim 6, wherein between steps a. and b. there is an additional step comprising harvesting, storage and/or purification, of the Leptospira culture. 